In our projection, we intend to measure the pharmacokinetics of prednisone and prednisolone in renal transplant recipients. To do this, we will employ a drug assay utilizing high pressure liquid chromatography (HPLC). Along with this technique, equilibrium dialysis will be incorporated to allow for the measurement of total and free drug levels. We intend to measure interindividual differences of prednisone/prednisolone pharmacokinetics depending on concomitant drug, meal or antacid ingestion. Various prednisone preparations can be tested utilizing this technique. In addition, correlations with biologic side-effects (Cushingoid appearance or lymphocyte and monocyte effects) will be made. These correlations will give important information regarding prednisone's in-vivo activity in renal transplant patients. Original studies involving prednisone administration (with and without concomitant azathioprine) will offer new insights into lymphocyte effects of these two common post-transplant immunosuppressants. It is anticipated that other potentially important clinical conditions can be studied. These would include prednisone/prednisolone metabolism during uremia, nephrosis, and during liver dysfunction (all these conditions are potential complications following renal transplantation).